Acoustic device

ABSTRACT

Acoustic devices, particularly musical instruments, having a soundboard formed from expanded polycarbonate, methods of manufacture of same, and the use of specific soundboards in the manufacture of acoustic devices.

This is a nationalization of PCT/GB00/03073 filed Aug. 9, 2000 andpublished in English.

FIELD OF THE INVENTION

The present invention concerns acoustic devices, particularly musicalinstruments, having a new and improved soundboard, methods ofmanufacture of same, and the use of specific soundboards in themanufacture of acoustic devices.

BACKGROUND OF THE INVENTION

For a long time it has been desired to produce acoustic devices,particularly musical instruments such as guitars, using soundboardsconstructed from synthetic polymers rather than wood as is traditionallydone. Such devices would be relatively simple and inexpensive tomanufacture and the production of devices having reproducible acousticproperties would be reduced from the complex skill-dependent job of anartisan to a controllable manufacturing process.

There have been many attempts to produce musical instruments havingsynthetic polymer-based soundboards, e.g. U.S. Pat. No. 4,353,862, U.S.Pat. No. 4,364,990, U.S. Pat. No. 4,429,608, U.S. Pat. No. 4,969,381,U.S. Pat. No. 4,873,907, U.S. Pat. No. 4,188,850, U.S. Pat. No.4,185,534, U.S. Pat. No. 4,213,370, U.S. Pat. No. 4,290,336, U.S. Pat.No. 4,334,452, U.S. Pat. No. 5,469,769, U.S. Pat. No. 5,804,746 and U.S.Pat. No. 4,290,336.

However, such instruments have typically suffered from the problem thatthey have been of a complex construction (for example with soundboardsrequiring carbon fibre or glass fibre reinforcements), are costly tomanufacture, and have a sound quality not comparable to sound producedby instruments having the traditional wooden soundboard.

SUMMARY OF THE INVENTION

The present inventors have overcome the prior art disadvantages,producing musical instruments having polymer-based soundboards which arecapable of producing sound of comparable quality to that produced bywooden soundboards. The materials used are readily available and may beused to produce any desired acoustic device having a soundboard.

According to the present invention there is provided an acoustic devicehaving a soundboard comprising expanded polycarbonate.

The expanded polycarbonate may be provided in the form of a sheet.

The soundboard may have a cellular rigid foam structure.

The soundboard may have a density of 500-700 kg/m³, for example 650kg/m³.

The soundboard may have a tensile strength of about 20 MPa.

The soundboard may have a flexural strength of about 30 N/mm².

One expanded polycarbonate material which is particularly useful isFOREX-EPC E 50.650 (Airex AG, Switzerland; SBA Ltd, Leicester, UK). Ithas a closed cell rigid foam structure, an apparent density (DIN 53479)of 650 kg/m³, a tensile strength (DIN 53455) of 20 MPa, elongation atbreak (DIN 53455) of at least 10%, an E-Modulus in tension (DIN 53457)of 1000 MPa and in flexure (DIN 53457) of 1200 MPa, a flexural strength(DIN 53452) of 30 N/mm², is unbreakable on impact (DIN 53453),dimensional changes (DIN 16927) of ±0% at 120 minutes at 70° C., −0.5%at 75 minutes at 140° C. (MD) and +0.4% at 75 minutes at 140° C. (TD),and water absorption (DIN 53495) of less than 1% (W3—100° C. 30minutes).

Although it has previously been suggested in the art to use foams in theconstruction of e.g. guitars, it has never been suggested to useexpanded polycarbonates. For example, U.S. Pat. No. 4,185,534 suggestsusing polystyrene and other homopolymers and copolymers derived fromhydrocarbon vinyl monomer. Accoustic tests conducted by the inventorsusing an expanded PVC (Foamex—Airex AG, Switzerland; SBA Ltd, Leicester,UK) were found to produce a very “dull” sound which was unacceptable.Non-expanded polystyrene was also tested and found to produce a very“tinny” sound which was also unacceptable.

In certain of the prior art, the use of foams is disclosed but this istypically in the manufacture of solid-bodied instruments and nothollow-bodied ones having a soundboard.

It is typically found with traditional wooden instruments having asoundboard that they have “dead spots” or emit “wolf tones”, which areparticular frequencies that either respond very poorly or are muchlouder than the notes of other frequencies. This problem can bemitigated or avoided completely using the soundboards of the presentinvention.

The expanded polycarbonates used in the acoustic devices of the presentinvention have excellent acoustic properties allowing for theconstruction of e.g. stringed instruments such as guitars (see below)which have a quality of sound at least as good as instruments havingwooden soundboards.

Naturally the exact acoustic properties of expanded polycarbonates willvary with e.g. their apparent density, tensile strength and flexuralstrength. Other factors such as the size of bubbles in the foam, eitheropen or closed cells, as well as the gas or gases contained in the foamare also important. Nitrogen is typically used to expand thepolycarbonate into the foam structure, but other gases may equally beused. For example, halogens such as argon, neon and helium. Othernormally gaseous (under normal atmospheric temperature and pressure)elements and compounds may also be used (subject to any undesiredreactions with the polycarbonate) and will be readily apparent to oneskilled in the art, for example as disclosed in e.g. U.S. Pat. No.4,185,534.

As well as forming the soundingboard of the acoustic device out of anexpanded polycarbonate such as a polycarbonate sheet, the physicalcharacteristics of the expanded polycarbonate may vary from point topoint. For example, if the acoustic device is a guitar, the expandedpolycarbonate soundboard may vary in thickness across its width or alongits length. Similarly the size and/or density of bubbles may be varied.

The acoustic device may be a guitar as discussed above, or it may be anyother musical instrument, particularly a stringed musical instrument,having a soundboard. For example, it may be a violin, mandolin, bass,lute, dulcimer, harp or piano.

The acoustic device may equally be any other device having a soundboard,for example devices requiring sound resonance (amplification) such asloudspeakers, drums or alarm systems.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further apparent from the following description,with reference to the several figures of the accompanying drawings,which show, by way of example only, forms of guitar according to thepresent invention.

Of the Figures:

FIG. 1 shows a front view of a first embodiment of a guitar;

FIG. 2 shows a front view of a second embodiment of a guitar; and

FIG. 3 shows a side view of the guitars in FIGS. 1 and 2.

Guitar 10 incorporating a soundboard according to the present inventionhas a general construction as shown in British Registered Designs Nos.2074916 (guitar body) and 2074917 (guitar bridge).

Guitar 10 comprises a wooden neck 20, head 30 and fretboard 40.Soundboard 50 comprises FOREX-EPC E 50.650 having outer edge 51 andinner edge 52 defining sound-hole 53. Underside bracing of soundboard 50is provided by a clear Lexan-polycarbonate brace 60.

Bridge 70 comprises Lexan. Sides 80 and back 90 comprise a single pieceepoxy glass fibre moulding. Soundboard 50, brace 60, bridge 70 and sides80/back 90 and bonded together using methylmethacrylate adhesive.

In a first embodiment of guitar 10 provided in FIG. 1, a patternconstruction for the main structural brace 60 is shown. Additionalsmaller braces (not shown) are used to distribute vibrations of thesoundboard 50.

A second embodiment of the guitar 10 is provided in FIG. 2. Here, brace60 is in a slightly V-shaped pattern. The pattern of brace 60 accordingto this second embodiment may be more suited for production manufactureof guitar 10. In one variation (not shown) of the second embodiment, thepattern of brace 60 will be parallel rather than slightly V-shaped.

It will be appreciated that it is not intended to limit the invention tothe above example only, many variations, such as might readily occur toone skilled in the art, being possible, without departing from the scopethereof as defined by the appended claims.

1. An acoustic device of a sound producer, said acoustic devicecomprising a body having a resonance chamber including a soundboard madeof expanded polycarbonate having a foamed structure.
 2. The acousticdevice according to claim 1, wherein said soundboard comprises anexpanded polycarbonate sheet.
 3. The acoustic device according to claim1, wherein said soundboard has a cellular rigid foam structure.
 4. Theacoustic device according to claim 1, wherein said soundboard has atensile strength of about 20 Mpa.
 5. The acoustic device according toclaim 1, wherein the body is a musical instrument.
 6. The acousticdevice according to claim 5, wherein the body is a stringed musicalinstrument.
 7. The acoustic device according to claim 6, wherein thebody is a stringed musical instrument selected from the group comprisingguitar, violin, mandolin, base, lute, dulcimer, harp and piano.
 8. Anacoustic device comprising a soundboard having a density of 500-700kg/m³ and made of expanded polycarbonate having a foamed structure. 9.The acoustic device according to claim 8, wherein said soundboard has adensity of 650 kg/m³.
 10. An acoustic device comprising a soundboardhaving a tensile strength of about 20 Mpa and made of expandedpolycarbonate having a foamed structure.
 11. An acoustic devicecomprising a soundboard having a flexural strength of about 30 N/mm² andmade of expanded polycarbonate having a foamed structure.
 12. Anacoustic device comprising a soundboard including a density of 650kg/m³, a tensile strength of about 20 Mpa, a flexural strength of about30 N/mm² and made of expanded polycarbonate having a foamed structure.